I don't have a specific dollar amount goal for my side hustle income. My goal is to have my side hustle income cover all of my discretionary personal spending. Things like: clothes, hair, make-up, massages, dinners out with friends, work lunches, books, hiking gear etc. I just set this goal a few months ago and so far it is going well. I've had to cover a few discretionary spends out of my regular paycheck, but those were small and didn't amount to much. Next year, I plan to be more focused on this goal, not allowing myself any personal spending that is not paid for by side hustle income.
I've found this approach to be more motivating than just setting a dollar amount goal. I like that it allows me to devote all of my regular paycheck to either necessities (which for me are: mortgage, utilities, food, car gas/insurance, child care, my kids' activities, and vacations) or after-tax savings (which either goes to college funds, brokerage account, or long-term savings for big expenses like car replacement or home improvement). If things go well next year, I'd like to expand my goal to have my side hustle income cover my discretionary personal spending and vacations. The year after that I'd like to add my children's expenses and my car expenses. The year after that, food and utilities. At that point, I'll mostly just have my mortgage left. Once I get to that point, my stash should cover my basic expenses and I will semi-FIRE or seriously downshift to focus my side hustles exclusively.